Tomoaki Osugi

The Polycomb-group gene Rae28 sustains Nkx2.5/Csx expression and is essential for cardiac morphogenesis

The Polycomb-group (PcG) gene Rae28 is a mammalian homologue of the Drosophila gene polyhomeotic. PcG genes are known to maintain transcription states, once initiated, probably by regulating chromatin structure. Since homozygous Rae28-deficient (Rae28(-/-)) mice displayed cardiac anomalies similar to congenital heart diseases in humans, we examined the role of Rae28 in cardiac morphogenesis at the molecular level. In Rae28(-/-) embryos, expression of the cardiac selector gene Nkx2.5/Csx (Nkx2.5) was initiated properly but was not sufficiently sustained later in development. This impaired expression of Nkx2.5 in the maintenance phase proved to have a crucial effect on cardiac morphogenesis, as demonstrated by the results of a genetic complementation experiment in which the cardiac anomalies were suppressed by overexpression of human NKX2.5/CSX1 in Rae28(-/-) embryos. Ubiquitous expression of exogenous Rae28 likewise restored the impaired Nkx2.5 expression in Rae28(-/-) embryos, further supporting the notion that Rae28 sustains Nkx2.5 expression in cardiomyocytes. Thus, our data show that a mammalian PcG gene can play a key role in organogenesis by helping to maintain the expression of a selector gene.

Bcl-xl reduces doxorubicin-induced myocardial damage but fails to control cardiac gene downregulation

OBJECTIVE We recently reported that doxorubicin (Dox), an effective anti-cancer drug, induces apoptosis in cardiac myocytes in association with reduction of Bcl-xl expression. In the present study, we further examined whether overexpression of Bcl-xl ameliorates Dox-induced cardiac myocyte damage. METHODS AND RESULTS Overexpression of the Bcl-xl gene by adenovirus vector resulted in an 11-fold increase in Bcl-xl protein in neonatal rat cardiac myocytes (BCL) compared to that in cells with beta-galactosidase gene transfection (CTL). Although Dox treatment generated similar amounts of reactive oxygen species (ROS) in BCL and CTL, cell viability was maintained and the number of apoptotic cardiac myocytes was significantly decreased in BCL. Cytochrome c release and enhanced caspase-3 activity after Dox treatment were significantly suppressed and Bax expression level was decreased in BCL. Cardiac-specific gene expression is known to be inhibited by Dox. The expression of cardiac alpha-actin and sarcoplasmic reticulum Ca(2+)-ATPase 2a mRNA was equally inhibited in BCL and CTL after Dox treatment. CONCLUSIONS Overexpression of Bcl-xl in cardiac myocytes failed to regulate Dox-induced ROS generation and cardiac-specific gene downregulation but inhibited apoptosis accompanied by reduction of Bax protein.

Overexpression of Polycomb-Group Gene rae28 in Cardiomyocytes Does Not Complement Abnormal Cardiac Morphogenesis in Mice Lacking rae28 But Causes Dilated Cardiomyopathy

The Polycomb-group genes (PcG) are widely conserved from Drosophila to mammals and are required for maintaining positional information during development. The rae28 gene (rae28) is a member of the mouse PcG. Mice deficient in rae28 (rae28−/−) demonstrated that rae28 has a role not only in anteroposterior patterning but also in cardiac morphogenesis. In this study we generated transgenic mice with ubiquitous or cardiomyocyte-specific exogenous rae28 expression. Genetic complementation experiments with these transgenic mice showed that ubiquitous expression of rae28 could reverse the cardiac anomalies in rae28−/−, whereas cardiomyocyte-specific expression of rae28 could not, suggesting that rae28 is involved in cardiac morphogenesis through a noncardiomyocyte pathway. Interestingly, however, cardiomyocyte-specific overexpression of rae28 caused dilated cardiomyopathy, which was associated with cardiomyocyte apoptosis, abnormal myofibrils, and severe heart failure. Cardiac expression of rae28 was predominant in the early embryonic stage, whereas that of the other PcG members was relatively constitutive. Because rae28 forms multimeric complexes with other PcG proteins in the nucleus, it is presumed that constitutive cardiomyocyte-specific rae28 overexpression impaired authentic PcG functions in the heart. rae28-induced dilated cardiomyopathy may thus provide a clue for clarifying the direct role of PcG in the maintenance of cardiomyocytes.

Specific Cardiomyopathy Caused by Multisystemic Lipid Storage in Jordan’s Anomaly

A 28-year-old Japanese man was admitted in 1996 with persistently high levels of serum creatine kinase (CK), glutamic oxaloacetic transaminase (GOT), and glutamic pyruvic transaminase (GPT). Physical examination revealed no skin disorder, but showed neurosensory hearing loss and early fatigability. The CK level was 1298 U/L (normal <90 U/L), the GOT level 73 U/L (normal <30 U/L), and the GPT level 79 U/L (normal <30 U/L) on admission. The patient’s serum carnitine level was 1.57 mg/dL (normal 1.22 to 1.86 mg/dL). Typical findings of Jordan’s …

A case of hypereosinophilic syndrome presenting mid-ventricular obstruction

Abstract A 59-year-old man with hypereosinophilic syndrome (HES) who had been maintained with low-dose prednisolone for 5 years developed the characteristic features of hypertrophic cardiomyopathy. Left ventricular endomyocardial biopsy revealed no eosinophilic infiltration but extensive myocardial fibrosis. Cardiac involvement in HES presents as endocardial fibrosis, resulting in a clinical presentation of restrictive cardiomyopathy. HES heart disease can also present dilated cardiomyopathy, but myocardial hypertrophy has only rarely been noted in conjunction with HES. This report concerns a patient with HES who had clinical and hemodynamic evidence of asymmetric septal hypertrophy with mid-ventricular obstruction.